Pulsed laser deposition of Bismuth Telluride compounds for human body energy scavengers

The world wide research interest in Bismuth Telluride thin films is due to the fact that they are the most commonly efficient thermoelectric materials at temperatures as low as room temperature, which is typically suitable for implementing such thin films through the fabrication of miniaturized thermoelectric generators and human body energy scavengers. This work aims to characterize various Bismuth Telluride -based thin films deposited by Pulsed Laser Deposition technique in order to optimize their thermoelectric performance represented in their thermoelectric figures of merit. This has been achieved by investigating the electrical and thermoelectric properties of the deposited thin films as well as studying the structural properties of such thin films that is necessary for future micromachining and fabrication of energy scavengers; the results of this effort are really promising. The first chapter is an introductory overview concerning thermoelectric effects and thermoelectric generators. The second chapter deals with the different deposition techniques and the reasoning behind the employment of PLD to deposit Bismuth Telluride thin films. The third chapter includes some of Bismuth Telluride chemical and physical properties in addition to a literature survey of what other groups have already achieved concerning this material. The fourth chapter covers all the experiments and includes the results of this work. Finally, the fifth chapter includes the summary, conclusion and recommendation for future progress in this topic

Application of Microsystems Technology in the Fabrication of Thermoelectric Micro-Converters

The use of thin-film deposition techniques with microsystems technologies renewed the interest in the thermoelectricity in the last years. Integration of efficient solid-state thermoelectric (TE) microdevices with microelectronics is desirable for local cooling and, since they can be used to stabilise the temperature of devices, decrease noise levels and increase operation speed. Their use in thermoelectric microgeneration (energy harvesting) can also supply energy to low power consumption electronic devices. In this chapter, the fabrication of thermoelectric microconverters is compared, both on materials from thin-film composites to supperlattice structures, and on its fabrication techniques

Thermoelectric generator and solid-state battery for stand-alone microsystems

This paper presents a thermoelectric (TE) generator and a solid-state battery for powering microsystems. Prototypes of TE generators were fabricated and characterized. The TE generator is a planar microstructure based on thin films of n-type bismuth telluride (Bi2Te3) and p-type antimony telluride (Sb2Te3), which were deposited using co-evaporation. The measurements on selected samples of Bi2Te3 and Sb2Te3 thin films indicated a Seebeck coefficient in the range of 90–250 μV K−1 and an in-plane electrical resistivity in the range of 7–17 μÄ m. The measurements also showed TE figures-of-merit, ZT, at room temperatures (T = 300 K) of 0.97 and 0.56, for thin films of Bi2Te3 and Sb2Te3, respectively (equivalent to a power factor, PF, of 4.87 mW K−2 m−1 and 2.81 mW K−2 m−1). The solid-state battery is based on thin films of: an anode of tin dioxide (SnO2), an electrolyte of lithium phosphorus oxynitride (LixPOyNz, known as LiPON) and a cathode of lithium cobaltate (LiCoO2, known as LiCO), which were deposited using the reactive RF (radio-frequency) sputtering. The deposition and characterization results of these thin-films layers are also reported in this paper.This work was fully supported by FCT/PTDC/EEA-ENE/66855/2006 project

Resonant Thermoelectric Nanophotonics

Photodetectors are typically based either on photocurrent generation from electron–hole pairs in semiconductor structures or on bolometry for wavelengths that are below bandgap absorption. In both cases, resonant plasmonic and nanophotonic structures have been successfully used to enhance performance. Here, we show subwavelength thermoelectric nanostructures designed for resonant spectrally selective absorption, which creates large localized temperature gradients even with unfocused, spatially uniform illumination to generate a thermoelectric voltage. We show that such structures are tunable and are capable of wavelength-specific detection, with an input power responsivity of up to 38 V W^(–1), referenced to incident illumination, and bandwidth of nearly 3 kHz. This is obtained by combining resonant absorption and thermoelectric junctions within a single suspended membrane nanostructure, yielding a bandgap-independent photodetection mechanism. We report results for both bismuth telluride/antimony telluride and chromel/alumel structures as examples of a potentially broader class of resonant nanophotonic thermoelectric materials for optoelectronic applications such as non-bandgap-limited hyperspectral and broadband photodetectors

SYNTHESIS AND PROPERTIES OF NANOCRYSTALLINE BI-TE BASED THERMOELECTRIC MATERIALS FOR ENERGY APPLICATION

Thermoelectric phenomenon is the science associated with converting thermal energy into electricity based on the Seebeck effect. Bismuth telluride Bi2Te3 is currently considered to be the state-of-the art thermoelectric material with high efficiency for low temperature applications and is therefore attractive for energy harvesting processes. Nanostructures thermoelectric materials provide a novel way to enhance thermoelectric properties and are considered to be the efficient building blocks for thermoelectric devices. In this work, n- and p-type bulk nanocrystalline Bismuth telluride thermoelectric materials were prepared by mechanical alloying / ball milling technique. The produced nano-crystalline powder were then consolidated using hot compaction under inert atmosphere. The novel processing of these materials maintained the nanostructure in both n- and p-type. Structural properties of the n- and p-types were characterized using X ray diffraction, scanning electron microscopy and transmission electron microscope. These techniques proved that the average grian size of the milled thermoelectric materials was about 20 nm. Accordingly, a Significant improvement in the figure of merit (ZT) is achieved through significant lattice thermal conductivity reduction and Seebeck coefficient improvement. The maximum ZT value for the n-type nanocrystalline thermoelectric was 1.67 at 373 K while the maximum ZT value for the p-type was 1.78 at the same temperature. These values are considered to be the highest values reported for similar materials. Evaluation of the mechanical properties was also performed through microhardness measurement using Vickers micro-hardness test, which shows an enhancement in mechanical properties for the produced materials

Fabrication, Characterization, Modeling and Testing of a Nanostructured Bulk Thermoelectric Cooler

New generation micro/nano devices are emerging to monitor, control and act on living systems. Particularly, in the field of cryobiology, there is a need to monitor and control temperature at the cellular level. An important step towards achieving this aim is to fabricate a novel bulk nanostructured thermoelectric cooler (TEC). As a first step towards achieving efficient localized control of temperature in biological systems, Bismuth-telluride (Bi2Te3) and Antimony-Telluride (Sb2Te3) arrays of nanowires and nanotubes were fabricated, characterized and modeled. A thermal conductivity model originally developed by Dames and Chen for superlattice nanowires was extended to nanotubes. Based on this model thermal conductivity of Bi2Te3 and Sb2Te3 nanowire or nanotube is determined. Lumped parameter model was also used to determine the performance of a device composed of nanowires or nanotubes. The modeling results suggest that nanotubes would yield higher reduction in thermal conductivity compared to nanowires. Bi2Te3 and Sb2Te3 arrays of nanowires and nanotubes were electrodeposited into the nanochannels of the polycarbonate template as n-type and p-type thermoelectric leg elements of the bulk thermoelectric cooler, respectively. SEM, XRD and WDS were employed to characterize the fabricated Bi2Te3 and Sb2Te3 nanowire or nanotube arrays. A custom built device is developed to characterize the Seebeck coefficient of the electrodeposited nanowires or nanotubes. The Seebeck coefficient values of Sb2Te3 nanowire and nanotube arrays were found to be +359 µV K-1 and +332 µV K-1, respectively. The positive Seebeck coefficient values indicated that electrodeposited Sb2Te3 nanowires and nanotubes were p-type. The Seebeck coefficient values of Bi2Te3 nanowire and nanotube arrays were found to be -118 µV K-1 and -143 µV K-1, respectively. The negative Seebeck coefficient values indicated that electrodeposited Bi2Te3 nanowire and nanotube arrays were n-type. The electrical resistance measurements confirmed that Bi2Te3 and Sb2Te3 nanowire or nanotube arrays resistance were semiconductors. A bulk nanostructured TEC is assembled using the best Bi2Te3 (n-type) and Sb2Te3 (p-type) nanowire or nanotube arrays. The ZT of the thus assembled device is determined by “Harmans Technique”. It is found that a combination of Bi2Te3 nanowires and Sb2Te3 nanotubes yielded highest ZT of around 0.4 at room temperature. Results suggest that there is clearly a need to significantly improve the performance of the nanostructured bulk TEC to compete with commercially available vapor compression coolers